pressure at fuel cap

[luapyrellod]

Hi all, have just filled up with fuel and driven home with the intention of putting some injector cleaner in the tank, but on trying to unscrew the fuel cap found that petrol is being forced out through the filler neck at pressure, anyone else had this problem?
This is the first time I have filled the tank right up
I have used the standard tank and cut the original metal filler pipe down to fit so it now does not have the ball valve in it anymore which I think most people have done ?
The fuel cap is the standard screw cap that came with the mx5 and has been positioned on the top of the rear cover and not through the side like Stuart has done, so my cap is above the top of the tank so it's not leakage because the pipe is too low.
Any help would be appreciated.

[mikesexocet]

Hi,

This can happen if the vent on the top of the tank is blocked. The vapour can't escape out of the top of the tank and so forces the fuel back out the filler.

Just a thought.

Mike

[p5curly]

I was told this was common and temperature difference can make it do that too